LIBRARY VERSION

Returns a string identifying the version of the netCDF library, and
when it was built, like: "3.1a of Aug 22 1996 12:57:47 $".

The RCS ident(1) command will find a string like
"$Id: @(#) netcdf library version 3.1a of Sep 6 1996 15:56:26 $"
in the library. The SCCS what(1) command will find a string like
"netcdf library version 3.1a of Aug 23 1996 16:07:40 $".

FILE OPERATIONS

Creates a new netCDF dataset at path,
returning a netCDF ID in ncid.
The argument cmode may include the bitwise-or
of the following flags:
NF_NOCLOBBER
to protect existing datasets (default
silently blows them away),
NF_SHARE
for synchronous dataset updates for classic format files
(default is to buffer accesses),

When a netCDF dataset is created, is is opened
NF_WRITE.
The new netCDF dataset is in define mode.
NF_64BIT_OFFSET.
to create a file in the 64-bit offset format
(as opposed to classic format, the default).
NF_TRUE to create a netCDF-4/HDF5 file,
and NF_CLASSIC_MODEL to guarantee that netCDF-4/HDF5 files maintain compatibility
with the netCDF classic data model.

Opens a existing netCDF dataset at path
returning a netCDF ID
in ncid.
The type of access is described by the mode parameter,
which may include the bitwise-or
of the following flags:
NF_WRITE
for read-write access (default
read-only),
NF_SHARE
for synchronous dataset updates (default is
to buffer accesses), and
NF_LOCK
(not yet implemented).

As of NetCDF version 4.1, and if TRUE support was enabled
when the NetCDF library was built, the path parameter
may specify a TRUE URL. In this case, the access mode is
forced to be read-only.

The argument referenced by chunksize controls a space versus time
tradeoff, memory allocated in the netcdf library versus number of system
calls.
Because of internal requirements, the value may not be set to exactly
the value requested.
The actual value chosen is returned by reference.
Using the value NF_SIZEHINT_DEFAULT causes the library to choose a
default.
How the system choses the default depends on the system.
On many systems, the "preferred I/O block size" is available from the
stat() system call, struct stat member st_blksize.
If this is available it is used. Lacking that, twice the system pagesize
is used.
Lacking a call to discover the system pagesize, we just set default
chunksize to 8192.

The chunksize is a property of a given open netcdf descriptor
ncid, it is not a persistent property of the netcdf dataset.

As with nf__open(), the path parameter
may specify a TRUE URL, but the tuning parameters are ignored.

integer function nf_redef(integer ncid)

(Corresponds to ncredf() in version 2)

Puts an open netCDF dataset into define mode,
so dimensions, variables, and attributes can be added or renamed and
attributes can be deleted.

integer function nf_enddef(integer ncid)

(Corresponds to ncendf() in version 2)

Takes an open netCDF dataset out of define mode.
The changes made to the netCDF dataset
while it was in define mode are checked and committed to disk if no
problems occurred. Some data values may be written as well,
see "VARIABLE PREFILLING" below.
After a successful call, variable data can be read or written to the dataset.

Caution: this function exposes internals of the netcdf version 1 file
format.
It may not be available on future netcdf implementations.

The current netcdf file format has three sections,
the "header" section, the data section for fixed size variables, and
the data section for variables which have an unlimited dimension (record
variables).
The header begins at the beginning of the file. The index
(offset) of the beginning of the other two sections is contained in the
header. Typically, there is no space between the sections. This causes
copying overhead to accrue if one wishes to change the size of the
sections,
as may happen when changing names of things, text attribute values,
adding
attributes or adding variables. Also, for buffered i/o, there may be
advantages
to aligning sections in certain ways.

The minfree parameters allow one to control costs of future calls
to nf_redef(), nf_enddef() by requesting that minfree bytes be
available at the end of the section.
The h_minfree parameter sets the pad
at the end of the "header" section. The v_minfree parameter sets
the pad at the end of the data section for fixed size variables.

The align parameters allow one to set the alignment of the beginning of
the corresponding sections. The beginning of the section is rounded up
to an index which is a multiple of the align parameter. The flag value
NF_ALIGN_CHUNK tells the library to use the chunksize (see above)
as the align parameter.
The v_align parameter controls the alignment of the beginning of
the data section for fixed size variables.
The r_align parameter controls the alignment of the beginning of
the data section for variables which have an unlimited dimension (record
variables).

The file format requires mod 4 alignment, so the align parameters
are silently rounded up to multiples of 4. The usual call,
nf_enddef(ncid)
is equivalent to
nf__enddef(ncid, 0, 4, 0, 4).

The file format does not contain a "record size" value, this is
calculated from the sizes of the record variables. This unfortunate fact
prevents us from providing minfree and alignment control of the
"records"
in a netcdf file. If you add a variable which has an unlimited
dimension,
the third section will always be copied with the new variable added.

integer function nf_sync(integer ncid)

(Corresponds to ncsnc() in version 2)

Unless the
NF_SHARE
bit is set in
nf_open() or nf_create(),
accesses to the underlying netCDF dataset are
buffered by the library. This function synchronizes the state of
the underlying dataset and the library.
This is done automatically by
nf_close() and nf_enddef().

integer function nf_abort(integer ncid)

(Corresponds to ncabor() in version 2)

You don't need to call this function.
This function is called automatically by
nf_close()
if the netCDF was in define mode and something goes wrong with the commit.
If the netCDF dataset isn't in define mode, then this function is equivalent to
nf_close().
If it is called after
nf_redef(),
but before
nf_enddef(),
the new definitions are not committed and the dataset is closed.
If it is called after
nf_create()
but before
nf_enddef(),
the dataset disappears.

integer function nf_close(integer ncid)

(Corresponds to
ncclos() in version 2)

Closes an open netCDF dataset.
If the dataset is in define mode,
nf_enddef()
will be called before closing.
After a dataset is closed, its ID may be reassigned to another dataset.

integer function nf_inq(integer ncid, integer ndims, integer nvars,

integer natts, integer unlimdimid)

integer function nf_inq_ndims(integer ncid, integer ndims)

integer function nf_inq_nvars(integer ncid, integer nvars)

integer function nf_inq_natts(integer ncid, integer natts)

integer function nf_inq_unlimdim(integer ncid, integer unlimdimid)

integer function nf_inq_format(integer ncid, integer formatn)

Use these functions to find out what is in a netCDF dataset.
Upon successful return,
ndims will contain the
number of dimensions defined for this netCDF dataset,
nvars will contain the number of variables,
natts will contain the number of attributes, and
unlimdimid will contain the
dimension ID of the unlimited dimension if one exists, or
0 otherwise.
formatn will contain the version number of the dataset <format>, one of
NF_FORMAT_CLASSIC, NF_FORMAT_64BIT, NF_FORMAT_NETCDF4, or
NF_FORMAT_NETCDF4_CLASSIC.

Adds a new dimension to an open netCDF dataset, which must be
in define mode.
name is the dimension name.
dimid will contain the dimension ID of the newly created dimension.

USER DEFINED TYPES

Users many define types for a netCDF-4/HDF5 file (unless the
NF_CLASSIC_MODEL was used when the file was creates). Users may
define compound types, variable length arrays, enumeration types, and
opaque types.

name should be big enough (NF_MAX_NAME)
to hold the dimension name as the name will be copied into your storage.
The length return parameter, len
will contain the size of the dimension.
For the unlimited dimension, the returned length is the current
maximum value used for writing into any of the variables which use
the dimension.

Renames an existing dimension in an open netCDF dataset.
If the new name is longer than the old name, the netCDF dataset must be in
define mode.
You cannot rename a dimension to have the same name as another dimension.

Writes an entire netCDF variable (i.e. all the values). The netCDF
dataset must be open and in data mode. The type of the data is
specified in the function name, and it is converted to the external
type of the specified variable, if possible, otherwise an
NF_ERANGE error is returned. Note that rounding is not performed
during the conversion. Floating point numbers are truncated when
converted to integers.

Reads an entire netCDF variable (i.e. all the values).
The netCDF dataset must be open and in data mode.
The data is converted from the external type of the specified variable,
if necessary, to the type specified in the function name. If conversion is
not possible, an NF_ERANGE error is returned.

Puts a single data value into a variable at the position index of an
open netCDF dataset that is in data mode. The type of the data is
specified in the function name, and it is converted to the external type
of the specified variable, if possible, otherwise an NF_ERANGE
error is returned.

Gets a single data value from a variable at the position index
of an open netCDF dataset that is in data mode.
The data is converted from the external type of the specified variable,
if necessary, to the type specified in the function name. If conversion is
not possible, an NF_ERANGE error is returned.

Writes an array section of values into a netCDF variable of an open
netCDF dataset, which must be in data mode. The array section is specified
by the start and count vectors, which give the starting index
and count of values along each dimension of the specified variable.
The type of the data is
specified in the function name and is converted to the external type
of the specified variable, if possible, otherwise an NF_ERANGE
error is returned.

Reads an array section of values from a netCDF variable of an open
netCDF dataset, which must be in data mode. The array section is specified
by the start and count vectors, which give the starting index
and count of values along each dimension of the specified variable.
The data is converted from the external type of the specified variable,
if necessary, to the type specified in the function name. If conversion is
not possible, an NF_ERANGE error is returned.

These functions are used for strided output, which is like the
array section output described above, except that
the sampling stride (the interval between accessed values) is
specified for each dimension.
For an explanation of the sampling stride
vector, see COMMON ARGUMENTS DESCRIPTIONS below.

These functions are used for strided input, which is like the
array section input described above, except that
the sampling stride (the interval between accessed values) is
specified for each dimension.
For an explanation of the sampling stride
vector, see COMMON ARGUMENTS DESCRIPTIONS below.

These functions are used for mapped output, which is like
strided output described above, except that an additional index mapping
vector is provided to specify the in-memory arrangement of the data
values.
For an explanation of the index
mapping vector, see COMMON ARGUMENTS DESCRIPTIONS below.

These functions are used for mapped input, which is like
strided input described above, except that an additional index mapping
vector is provided to specify the in-memory arrangement of the data
values.
For an explanation of the index
mapping vector, see COMMON ARGUMENTS DESCRIPTIONS below.

Unlike variables, attributes do not have
separate functions for defining and writing values.
This family of functions defines a new attribute with a value or changes
the value of an existing attribute.
If the attribute is new, or if the space required to
store the attribute value is greater than before,
the netCDF dataset must be in define mode.
The parameter len is the number of values from out to transfer.
It is often one, except that for
nf_put_att_text() it will usually be
len_trim(out).

For these functions, the type component of the function name refers to
the in-memory type of the value, whereas the xtype argument refers to the
external type for storing the value. An NF_ERANGE
error results if
a conversion between these types is not possible. In this case the value
is represented with the appropriate fill-value for the associated
external type.

Gets the
name of an attribute, given its variable ID and attribute number.
This function is useful in generic applications that
need to get the names of all the attributes associated with a variable,
since attributes are accessed by name rather than number in all other
attribute functions. The number of an attribute is more volatile than
the name, since it can change when other attributes of the same variable
are deleted. The attributes for each variable are numbered
from 1 (the first attribute) to
nvatts,
where nvatts is
the number of attributes for the variable, as returned from a call to
nf_inq_varnatts().

Copies an
attribute from one netCDF dataset to another. It can also be used to
copy an attribute from one variable to another within the same netCDF.
ncid_in is the netCDF ID of an input netCDF dataset from which the
attribute will be copied.
varid_in
is the ID of the variable in the input netCDF dataset from which the
attribute will be copied, or NF_GLOBAL
for a global attribute.
name
is the name of the attribute in the input netCDF dataset to be copied.
ncid_out
is the netCDF ID of the output netCDF dataset to which the attribute will be
copied.
It is permissible for the input and output netCDF ID's to be the same. The
output netCDF dataset should be in define mode if the attribute to be
copied does not already exist for the target variable, or if it would
cause an existing target attribute to grow.
varid_out
is the ID of the variable in the output netCDF dataset to which the attribute will
be copied, or NF_GLOBAL to copy to a global attribute.

Changes the
name of an attribute. If the new name is longer than the original name,
the netCDF must be in define mode. You cannot rename an attribute to
have the same name as another attribute of the same variable.
name is the original attribute name.
newname
is the new name to be assigned to the specified attribute. If the new name
is longer than the old name, the netCDF dataset must be in define mode.

Gets the value(s) of a netCDF attribute, given its
variable ID and name. Converts from the external type to the type
specified in
the function name, if possible, otherwise returns an NF_ERANGE
error.
All elements of the vector of attribute
values are returned, so you must allocate enough space to hold
them. If you don't know how much space to reserve, call
nf_inq_attlen()
first to find out the length of the attribute.

COMMON ARGUMENT DESCRIPTIONS

In this section we define some common arguments which are used in the
"FUNCTION DESCRIPTIONS" section.

integer ncid

is the netCDF ID returned from a previous, successful call to
nf_open() or nf_create()

character*(*) name

is the name of a dimension, variable, or attribute. The names of
dimensions, variables and attributes consist of arbitrary
sequences of alphanumeric characters (as well as underscore '_',
period '.' and hyphen '-'), beginning with a letter or
underscore. (However names commencing with underscore are reserved for
system use.) Case is significant in netCDF names. A zero-length name
is not allowed.

The maximum allowable number of characters
is NF_MAX_NAME.

integer xtype

specifies the external data type of a netCDF variable or attribute and
is one of the following:
NF_BYTE, NF_CHAR, NF_SHORT, NF_INT,
NF_FLOAT, or NF_DOUBLE.
These are used to specify 8-bit integers,
characters, 16-bit integers, 32-bit integers, 32-bit IEEE floating point
numbers, and 64-bit IEEE floating-point numbers, respectively.

is a vector of dimension ID's and defines the shape of a netCDF variable.
The size of the vector shall be greater than or equal to the
rank (i.e. the number of dimensions) of the variable (ndims).
The vector shall be ordered by the speed with which a dimension varies:
dimids(1)
shall be the dimension ID of the most rapidly
varying dimension and
dimids(ndims)
shall be the dimension ID of the most slowly
varying dimension.
The maximum possible number of
dimensions for a variable is given by the symbolic constant
NF_MAX_VAR_DIMS.

integer dimid

is the ID of a netCDF dimension.
netCDF dimension ID's are allocated sequentially from the
positive
integers beginning with 1.

integer ndims

is either the total number of dimensions in a netCDF dataset or the rank
(i.e. the number of dimensions) of a netCDF variable.
The value shall not be negative or greater than the symbolic constant
NF_MAX_VAR_DIMS.

integer varid

is the ID of a netCDF variable or (for the attribute-access functions)
the symbolic constant
NF_GLOBAL,
which is used to reference global attributes.
netCDF variable ID's are allocated sequentially from the
positive
integers beginning with 1.

integer natts

is the number of global attributes in a netCDF dataset for the
nf_inquire()
function or the number
of attributes associated with a netCDF variable for the
nf_varinq()
function.

specifies the indicial coordinates of the netCDF data value to be accessed.
The indices start at 1;
thus, for example, the first data value of a
two-dimensional variable is (1,1).
The size of the vector shall be at least the rank of the associated
netCDF variable and its elements shall correspond, in order, to the
variable's dimensions.

specifies the starting point
for accessing a netCDF variable's data values
in terms of the indicial coordinates of
the corner of the array section.
The indices start at 1;
thus, the first data
value of a variable is (1, 1, ..., 1).
The size of the vector shall be at least the rank of the associated
netCDF variable and its elements shall correspond, in order, to the
variable's dimensions.

specifies the number of indices selected along each dimension of the
array section.
Thus, to access a single value, for example, specify count as
(1, 1, ..., 1).
Note that, for strided I/O, this argument must be adjusted
to be compatible with the stride and start arguments so that
the interaction of the
three does not attempt to access an invalid data co-ordinate.
The elements of the
count vector correspond, in order, to the variable's dimensions.

specifies the sampling interval along each dimension of the netCDF
variable. The elements of the stride vector correspond, in order,
to the netCDF variable's dimensions (stride(1))
gives the sampling interval along the most rapidly
varying dimension of the netCDF variable). Sampling intervals are
specified in type-independent units of elements (a value of 1 selects
consecutive elements of the netCDF variable along the corresponding
dimension, a value of 2 selects every other element, etc.).

imap

specifies the mapping between the dimensions of a netCDF variable and
the in-memory structure of the internal data array. The elements of
the index mapping vector correspond, in order, to the netCDF variable's
dimensions (imap(1) gives the distance
between elements of the internal array corresponding to the most
rapidly varying dimension of the netCDF variable).
Distances between elements are specified in type-independent units of
elements (the distance between internal elements that occupy adjacent
memory locations is 1 and not the element's byte-length as in netCDF 2).

VARIABLE PREFILLING

By default, the netCDF interface sets the values of
all newly-defined variables of finite length (i.e. those that do not have
an unlimited, dimension) to the type-dependent fill-value associated with each
variable. This is done when nf_enddef()
is called. The
fill-value for a variable may be changed from the default value by
defining the attribute `_FillValue' for the variable. This
attribute must have the same type as the variable and be of length one.

Variables with an unlimited dimension are also prefilled, but on
an `as needed' basis. For example, if the first write of such a
variable is to position 5, then
positions
1 through 4
(and no others)
would be set to the fill-value at the same time.

This default prefilling of data values may be disabled by
or'ing the
NF_NOFILL
flag into the mode parameter of nf_open() or nf_create(),
or, by calling the function nf_set_fill()
with the argument NF_NOFILL.
For variables that do not use the unlimited dimension,
this call must
be made before
nf_enddef().
For variables that
use the unlimited dimension, this call
may be made at any time.

One can obtain increased performance of the netCDF interface by using
this feature, but only at the expense of requiring the application to set
every single data value. The performance
enhancing behavior of this function is dependent on the particulars of
the implementation and dataset format.
The flag value controlled by nf_set_fill()
is per netCDF ID,
not per variable or per write.
Allowing this to change affects the degree to which
a program can be effectively parallelized.
Given all of this, we state that the use
of this feature may not be available (or even needed) in future
releases. Programmers are cautioned against heavy reliance upon this
feature.

Determines whether or not variable prefilling will be done (see
above).
The netCDF dataset shall be writable.
fillmode is either NF_FILL
to enable prefilling (the
default) or NF_NOFILL
to disable prefilling.
This function returns the previous setting in old_fillmode.

MPP FUNCTION DESCRIPTIONS

Additional functions for use on SGI/Cray MPP machines (_CRAYMPP).
These are used to set and inquire which PE is the base for MPP
for a particular netCDF. These are only relevant when
using the SGI/Cray ``global''
Flexible File I/O layer and desire to have
only a subset of PEs to open the specific netCDF file.
For technical reasons, these functions are available on all platforms.
On a platform other than SGI/Cray MPP, it is as if
only processor available were processor 0.

To use this feature, you need to specify a communicator group and call
glio_group_mpi() or glio_group_shmem() prior to the netCDF
nf_open() and nf_create() calls.

Like nf__open() but allows the base PE to be set.
The argument pe sets the base PE at creation time. In the MPP
environment, nf__open() and nf_open() set the base PE to processor
zero by default.

integer function nf_inq_base_pe(integer ncid, integer pe)

Inquires of the netCDF dataset which PE is being used as the base for MPP use.
This is safe to use at any time.

integer function nf_set_base_pe(integer ncid, integer pe)

Resets the base PE for the netCDF dataset.
Only perform this operation when the affected communicator group
synchronizes before and after the call.
This operation is very risky and should only be contemplated
under only the most extreme cases.

ENVIRONMENT VARIABLES

NETCDF_FFIOSPEC

Specifies the Flexible File I/O buffers for netCDF I/O when executing
under the UNICOS operating system (the variable is ignored on other
operating systems).
An appropriate specification can greatly increase the efficiency of
netCDF I/O -- to the extent that it can actually surpass FORTRAN binary
I/O.
This environment variable has been made a little more generalized,
such that other FFIO option specifications can now be added.
The default specification is bufa:336:2,
unless a current FFIO specification is in operation,
which will be honored.
See UNICOS Flexible File I/O for more information.

MAILING-LISTS

Both a mailing list and a digest are available for
discussion of the netCDF interface and announcements about netCDF bugs,
fixes, and enhancements.
To begin or change your subscription to either the mailing-list or the
digest, send one of the following in the body (not
the subject line) of an email message to "majordomo@unidata.ucar.edu".
Use your email address in place of jdoe@host.inst.domain.